Field of the Invention
The present invention relates to an extendable and contractible flexible joint that includes a pair of flexible joint portions which is bendable and has a connection portion for a fluid transport pipe such as a water pipe or a plant pipe, and a connection sleeve that is fitted and connected across both the flexible joint portions.
Description of Related Art
Each of both of flexible joint portions of this type of an extendable and contractible flexible joint is made up of an outer joint body with a connection portion for a fluid transport pipe, and an inner joint body with a spherical outer circumferential surface slidably fitted to the spherical inner circumferential surface of the outer joint body.
In an extendable and contractible flexible joint in which the connection sleeve is formed integrally with the respective inner joint bodies of both the flexible joint portions, the connection sleeve is made up of an inner fitting sleeve and an outer fitting sleeve which are extendably and contractibly fitted and connected to each other.
A first annular protrusion protrudes from an intermediate portion of the outer circumferential surface of the inner fitting sleeve in the direction of a pipe axial line, and a second annular protrusion for restraining breakup protrudes from a tip end portion of the inner circumferential surface of the outer fitting sleeve so as to be able to come into contact with the first annular protrusion of the inner fitting sleeve in the direction of the pipe axial line. An extension and contraction allowance portion is made up of the first annular protrusion and the second annular protrusion such that relative movement between both the flexible joint portions in the direction of the pipe axial line is allowed in a set movement range (refer to Patent Document 1).
When an external force is applied to this extendable and contractible joint due to an earthquake, land subsidence, or the like, it is possible to absorb the external force while preventing the leakage of a pressure fluid caused by the breakup of configuration members of the extendable and contractible flexible joint by means of the extending and contracting motion of the extension and contraction allowance portion provided between the inner fitting sleeve and the outer fitting sleeve of the connection sleeve, and a bending motion (eccentric motion in a direction perpendicular to the pipe axial line) resulting from relative sliding between the spherical inner circumferential surface of the outer joint body and the spherical outer circumferential surface of the inner joint body, both which form each of the flexible joint portions.
However, when the pressure fluid flows from one of the flexible joint portions toward the other in this type of the extendable and contractible flexible joint, the extension and contraction allowance portion provided between the inner fitting sleeve and the outer fitting sleeve unnecessarily extends due to a fluid pressure, and thus the absorption capacity of the extendable and contractible flexible joint for an external tensile force is decreased, which is a problem.
For example, as illustrated in Patent Document 1, in the related art, there has been proposed a method in which the gap between both the flexible joint portions in the direction of the pipe axial line is maintained to be a set gap by inserting both screw portions of a bolt across a bolt insertion hole of an attachment protrusion that protrudes from the outer circumferential surface of the outer joint body of each of both the flexible joint portions, and fixing the attachment protrusion using nuts screwed onto both the screw portions of the bolt while the attachment protrusion being interposed between the nuts.